In many chemical engineering processes the deposition of particles from gaseous streams laden with pollutants and/or particles to either obtain a product or reduce emissions is a major step in the process. Particle filters are consequently used in many areas, in particular for removing particulates from the exhaust gas of internal combustion engines. In exhaust emission control systems, particularly for diesel engines, the particle filter is used to filter out most of the particles, mostly particulates, from the exhaust gas of the engine. The particulates accumulate on the particle filter, which causes its flow resistance to increase over time and impedes proper operation of the engine.
During operation of the engine, small amounts of the lubricating oil are inevitably burned together with the fuel. The oil additives that are usually added to the lubricating oil form non-combustible particulate compounds in the exhaust gas and accumulate on the particle filter as ash, which also contributes to the increase in the flow resistance of the particle filter over time.
A method which reverses or avoids the increase in the particle filter flow resistance caused by the accumulation of particulates is proposed in European Patent EP 0 341 832 B1. In this continuously operating method, the particulates deposited on the particle filter are oxidized or burned with the aid of the nitrogen dioxide present in the exhaust gas.
In addition to this continuous method, other methods of burning off particulates for the discontinuous regeneration of clogged particle filters are known. In these methods, special measures can be used to heat up the temperature of the exhaust gas from time to time to temperatures in excess of 550° C. while maintaining an oxidizing composition, which leads to the burning off of the particulates.
Since during normal operation of diesel engines, exhaust gas temperatures in excess of 500° C. are rarely reached, it is also known to use a fuel additive which lowers the particulate burn-off temperature. One example of this is disclosed in patent DE 40 41 127 C2. After the combustion process in the combustion chamber of the engine, the effective constituents of the fuel additive are still found in particle form in the exhaust gas and are deposited on the particle filter. The additive deposits have catalytic properties and cause a lowering of the particulate burn-off temperature. Therefore the flow resistance of the particle filter clog with particulates can be temporarily reduced again by using the regeneration or particulate burn-off processes mentioned.
Nevertheless, during the operating time of the particle filter, its flow resistance inevitably increases to undesirably high values as the ash particles that also accumulate on the particle filter cannot be removed by these particulate burn-off processes. It is therefore often recommended to remove the particle filter from the exhaust emission control system and replace it after a certain running time of the motor vehicle. To avoid this laborious measure, an operating method for a particle filter in which it is freed of ash by flushing with a liquid in a flushing process is proposed in the patent DE 43 13 132 C2. However, the ash usually forms a deposit that firmly adheres to the particle filter, making this flushing process difficult to carry out and often incomplete.
The present method provides a new method for operating a particle filter, in particular a particle filter of an internal combustion engine of a motor vehicle, with which ash particles can be removed effectively.
With particle deposition on surface filters a layer of filtrate or ash particles that increases as the process progresses forms on the surface of the filter medium. This layer is known as a dust cake or filter cake. This layer causes the pressure loss to increase with increasing filtration time. To maintain a commercially viable filtration operation, the layer of filtrate or ash particles must be periodically removed from the surface of the filter medium.
Many methods are known for the removal of the layer. As already mentioned, these include the thermal burn-off of a layer of particulates from the surface of the diesel particle filter and the back flushing of the filter with a fluid by flow reversal or by pressure surge regeneration. If the layer of filtrate or ash particles is to be removed by introducing flow forces, the force of adhesion of the layer of filtrate or ash particles must be overcome by the applied flow forces at the interface of the filter medium and the layer of filtrate or ash particles. A major contributory factor to the flow forces here is the through-flow resistance of the layer of filtrate or ash particles itself. Particle filters that are subjected to a layer of filtrate or ash particles generally have high pressure losses during the previous filtration step. Furthermore, if the forces of adhesion with respect to the filter medium are very high, layers of particles with low through flow resistance are only inadequately detached from the surface of the filter medium.
With the method according to the present disclosure, this disadvantage is to be overcome, so that the layer of filtrate or ash particles deposited on a filter medium can be largely or completely detached by flow forces.
The foregoing example of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.